The long term goal of this project is to obtain a better understanding of how alterations in the cellular response to UV-induced DNA damage in human preneoplastic keratinocytes result in genomic instability and the progression to a malignant phenotype. We will investigate whether or not the acquisition of p53 mutations results in altered cell cycle checkpoints in response to UV irradiation. We will generate cell populations of primary human keratinocytes expressing mutant p53 proteins or no p53 protein using a retroviral system. The ability of these cell populations to growth arrest in response to UV irradiation will be determined by flow cytometry analysis of DNA content. In addition, we will investigate whether or not p53 mutations affect the ability of keratinocytes to repair UV-induced DNA damage. The DNA repair capacity of the human keratinocyte populations will be assessed by clonogenic survival assay, host cell reactivation assay and strand- specific hybridizations. In summary, this project will investigate the involvement of p53 in the cell cycle checkpoint control and the repair of UV-induced DNA damage in human preinmortal keratinocytes. This research may lead to a better understanding of the genesis of skin cancer.